Presents the requirements for Two-Way Data Link Communication (TWDL) services. TWDL services include predeparture clearance@ clearances@ reports@ and requests. In addition to testing standards@ the document includes functional@ performance@ interface@ and equipment standards for ??ATCCOMM.?? The term ??ATCCOMM?? as used in this document includes all components and units@ including software@ necessary for the aircraft equipment to support TWDL services with an ATC ground system peer via the Aeronautical Telecommunications Network (ATN).